JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
    <li>A</li>
    <li>B</li>
    <li>C</li>
</ul>

<ul>
    <li>A</li>
    <li>B</li>
    <li>C</li>
</ul>

CSS

.selected {
    font-weight:bold;
}

JavaScript

$( document ).ready(function() {
    $('li').click(function() {
        $(this).closest('ul').find('li').removeClass('selected');
        $(this).addClass('selected');
    });
});